Magnet strip conductor

ABSTRACT

A magnet strip conductor comprising a thin strip of electrically conductive metal whose edges are contoured to be tangent to the adjoining flat faces of the strip and to have an intermediate portion having a smaller radius of curvature than the tangent portion, all of the flat and contoured surfaces of the strip being completely covered with a coating of insulating material.

United States Patent Inventors Donald H. Osborn Rome; Robert F. Freeman, Boonville, N.Y. Appl. No. 853,034 Filed Aug. 26, 1969 Patented Jan. 26, 1971 Assignee Revere Copper and Brass Incorporated New York, N.Y. a corporation of Maryland MAGNET STRIP CONDUCTOR 3 Claims, 5 Drawing Figs.

US. Cl 174/119, 336/223 Int. Cl 1101b 7/08, H0 1 j 27/32 [50] Field of Search 336/223; 174/117,l17.ll,ll9

[56] References Cited UNITED STATES PATENTS 3,501,728 3/1970 Barriball 174/1 19X Primary Examiner-L. A Goldberg Attorney-Pennie, Edmonds, Morton, Taylor and Adams ABSTRACT: A magnet strip conductor comprising a thin strip of electrically conductive metal whose edges are contoured to be tangent to the adjoining flat faces of the strip and to have an intermediate portion having a smaller radius of curvature than the tangent portion, all of the flat and contoured surfaces of the strip being completely covered with a coating of insulating material.

PATENIEnmzsun I 3558. 1 SHEETIUFZ O INVENTORS DONALD H. OSBORN ATT N EY 3 BY ROBERT F. FREEMAN MAGNET STRIP CONDUCTOR This invention relatesto magnet strip conductors and, more particularly, to a magnet strip conductor having an edge configuration such that it insures retention of an applied coating of insulating material during a fluid stage in the curing of said material.

A magnet strip conductor is an insulated electrically conductive metal strip of demanding specifications. The strip must be as thin as possible in order to permit a maximum number of winding turns in a given amount of space and it must be completely covered with a continuous film or coating of electrically insulating material. It is a well recognized fact, however, that the attainment of these characteristics is impeded by the tendency of the insulating material to pull away from the edges of the strip between the time the material is applied to the strip in the form of a fluid and the time that the material is sufficiently cured or hardened as to remain in place. To the extent that the insulating material pulls away from the edge, it leaves a noninsulated area, or at least a poorly insulated area, which cannot be tolerated in magnet and transformer windings, or the like, and to the extent that the material pulls away from one portion of the edge it simultaneously causes thickening of the insulating coating on the flat surfaces of the strip adjacent the edges.

Many expedients for making the-insulating film of a magnet,

strip conductor remain in place during its fluid phase have been proposed and used heretofore, as represented by US. Pat. Nos. 3,401,058 and 3,400,006, and these expedients have included rolling or grinding the edges of the strip to give them a rounded contour. When the ends of the rounded portion do not terminate in the planes of the flat surfaces of the strip, the resulting junction is a sharp edge, and even when great care is taken to avoid such an edge it must finally be rolled to reduce its sharpness to a minimum. Nevertheless, rounded edges which have been flattened at the junction of the round edge with the flat planar surface of the strip tend to have a residual promontory which is difficult to cover with insulating material, and even when it is covered it constitutes a sufficient protuberance to promote arcing within a winding.

We have now discovered that a different and specific shape on the edge of a magnet strip conductor eliminates the aforementioned problems. Pursuant to the present invention, the magnet strip conductor comprises a thin strip of electrically conductive metal in which each of the two outside edges of the strip has a contour characterized by at least two substantially different radii of curvature, the portions of the contour adjoining the flat faces of the strip being tangent thereto and having a substantially larger radius of curvature than a portion of the contour intermediate said tangent portions. A coating of insulating material completely covers all of said flat and contoured surfaces of the strip.

These and other novel features of the magnet strip conductor of the invention will be more readily understood from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a cross-sectional view of the magnet strip conductor of the invention;

FIGS. 2, 3 and 4 are additional modifications, in simple line drawing, of the contoured edge of the strip embodying the invention; and

FIG. 5 is a partial cross-sectional view of a magnet winding embodying the conductor of FIG. 1.

As shown in FIG. 1, the substrate of the magnet strip conductor comprises a strip 5 of electrically conductive metal such as aluminum or copper or of potentially superconducting metal or alloy such as a columbium-zirconium alloy or the like. The thickness and width of the strip are of whatever dimensions are required for the current-carrying capacity expected of the strip under operating conditions. Present magnet and transformer winding specifications for strip conductors generally call for strips ranging from about 0.00075- to 0.linch thick, but the invention is not limited to strips of these dimensions. It is, however, a characteristic of all such strips that their width is a large multiple of their thickness and hence the term strip is used to describe them in contradistinction to conventional round, oval, square or oblong conductors. Our strip is thus characterized by two flat or planar surfaces 6 and 7 which are generally parallel to one another.

Pursuant to the invention, the edges of the flat-surfaced strip are provided with a specific contour 8. The shape of the contour, that is whether it is blunt or somewhat elongated, can vary considerably within the scope of the invention. The significant feature of this contour is that it is characterized by at least two substantially different radii of curvature, the portions of the contour adjoining the flat faces of the strip being tangent to these faces and having a substantially larger radius of curvature than a portion of the contour intermediate the aforementioned tangent portions, Such a contour is shown in FIG. 2 wherein the edge contour 8 adjoins the flat faces 6 and 7 of the strip. The terminal portions of the contour 8 are substantially tangent to the flat faces 6 and 7 where they adjoin these surfaces and are each formed with a radius of curvature indicated by r,. The intermediate portion of the contour 8 is formed with a radius of curvature, indicated by r;,, which is substantially smaller than r,. When a layer of applied resin 9 on the surfaces 6, 7 and 8 of the strip is heated to cause its curing, the resin passes through a fluid phase. That portion of the fluid resin over the portion of the contour having the smaller radius of curvature r appears to be subjected to greater separation stress than other portions of the fluid resin layer, and if this stress is sufficient to thin out the resin layer the thinning occurs predominatly over the contour of smaller radius of curvature. Thus, the portion of the contour of relatively smaller radius of curvature acts as a sacrificial portion which sequesters near it any relatively thin layer of fused resin which may form during curing. By positioning the portion of the contour ofsmaller radius of curvature intermediate the tangent portions of the contour of larger radius of curvature pursuant to our invention, any thinning of the applied resin layer, whether during its application or during its curing, occurs in a zone a which will be relatively remote from a surface of an adjacent magnet strip in a common winding.

The modifications of the edge contour of our invention shown in FIGS. 2, 3 and 4, have this same characteristic. In FIG. 2, the contour is that of an ellipse in which the radius of curvature is constantly decreasing from a maximum value of r at the tangent portion of the contour to the minimum value of F at the sharper end of the ellipse. The a axis of the ellipse (its horizontal axis in FIG. 2) can vary from about A; to 3 times that of its b axis (the thickness of the strip in FIG. 2). In FIG. 3, the contour is substantially that of a circle of radius r which has been blunted at its outermost section to create two contour portions with a smaller radius of curvature of r In FIG. 4, the blunting of a circular contour has such as to substantially flatten its outermost section and thus create, at the intersections of the flat portion with the rounded contour of radius r,, a portion of extremely small radius of curvature r Each of the aforementioned modifications of the edge contour of our invention functions substantially the same as that of the modification of FIG. 1 which is shown in winding form in FIG. 5. As can be seen, the portion of the edge contour having the smaller radius of curvature is located away from an adjacent winding turn. Thus, if any thinning of the insulating material layer 9 occurs, it will be substantially in a zone overlying the portion of the surface of the contour 8 having the smaller radius of curvature, and inasmuch as the portion of smaller radius of curvature is intermediate the two tangent ends of the contour 8 any thin portion of the insulating layer will be substantially intermediate the extremities of the flat faces 6 and 7 of the strip and substantially as remote as possible from these surfaces.

The contoured edges of the strip can be formed by a variety of techniques. In addition to being hand crafted, it can be formed readily by electrolytically etching or milling aconventional standard round-edge strip. We presently prefer to form the edge by a rolling procedure involving at least two rollforming stages. For example, an edge contour substantially that shown in FIG. 1 was produced by slitting electrical grade aluminum sheet to 5-inch width at 0.02l-inch gauge. Each edge was first formed by passing it through edge roll dies of 0.026-inch [.D. and by then roll reducing the strip gauge to 0.0l850.0l9 inch. Both edges were given a second roll forming with 0.02l inch l.D. roll dies, following which the strip was further roll reduced to about 0.0l9-inch gauge. The finished strip was annealed to zero temper. was cleaned and then electrophoretically coated with an acrylic-polyester cross-linking resin. The resin coating was cured and yielded an insulated magnet strip conductor capable of withstanding 1,000 volts breakdown and free of breakdown between adjacent turns when formed into a conventional magnet winding.

The insulating material used as the coating for the magnet strip shape of our invention is not limited to the aforementioned resin but can be any insulating material conventionally used heretofore. Generally, these materials are of organic composition and can comprise lacquers, enamels, superpolyamides, polyesters, and a wide variety of other resins having electrical insulating properties. These materials can be applied in any manner conductive to the formation of a smooth unifonn coating layer. Dipping is the least desirable from this point of view, but the specific shape of the edges of the strip pursuant to our invention makes possible a more uniform dipcoating layer of insulating material than could be obtained with edge configurations of the prior art. More uniform coatings can be obtained, however, by jet spraying, electrostatic spraying and electrophoretic deposition, all of which techniques are well known. The various coatings can be nor mally fluid when applied or they can be in the form of normally solid discrete particles suspended in a carrier medium. Drying'or curing of the applied coating can be by any conventional technique such as by baking or hot gas stream, or the like, but our present preference is for curing by induction heating of the metal substrate so as to evolve any volatiles from the inside of the coating layer toward the outside.

it will be appreciated, accordingly, that the magnet strip of our invention is characterized by an edge configuration such that the applied insulating material does not pull away or does not have to cover any irregular promontory on any portion of the strip surface, with the result that the finished strip is ideally suited for its intended use without danger of incipient break down or turn-to-turn arcing.

We claim:

1. A magnet strip conductor comprising a thin strip of electrically conductive metal, the two edges of the strip each having a contour characterized by at least two substantially different radii of curvature, the portions of said contour adjoining the flat faces of the strip being tangent thereto and having a substantially larger radius of curvature than a portion of the contour intermediate said tangent-portions, and a coating of insulating material completely covering all of said flat and contour surfaces of the strip.

-2. A magnet strip according to claim] in which said contour is in the form of an ellipse.

3. A magnet strip according to claim 2 in which the a axis of the ellipse has a dirriensioti ranging from about A; to 3 times that of its b axis. 

1. A magnet strip conductor comprising a thin strip of electrically conductive metal, the two edges of the strip each having a contour characterized by at least two substantially different radii of curvature, the portions of said contour adjoining the flat faces of the strip being tangent thereto and having a substantially larger radius of curvature than a portion of the contour intermediate said tangent portions, and a coating of insulating material completely covering all of said flat and contour surfaces of the strip.
 2. A magnet strip according to claim 1 in which said contour is in the form of an ellipse.
 3. A magnet strip according to claim 2 in which the a axis of the ellipse has a dimension ranging from about 1/3 to 3 times that of its b axis. 